Previous work done in this project has led to the establishment of quantitative physical models for the dissolution kinetics of apatites and dental enamel. These models have been used to make absolute correlations between rates of dissolution observed in experiments with suspensions of hydroxyapatite crystals and rates observed with compressed pellets of apatites or blocks of enamel. The models have also been useful in explaining observed morphology at both the single crystal level and at the lesion level. In addition, the models have provided a framework in which to study the response of enamel and apatite dissolution kinetics to foreign agents such as fluoride and dodecylamine hydrochloride (DDA). The quantitative (and sometimes qualitative, as well) interpretation of results in this past work has always depended on the nature of the apatite or enamel preparation used and differences between preparations were simply noted. Recent work using DDA as a probe has led to the postulation of a unified model for apatite dissolution with which we will endeavor to construct systematic relationships between dissolution kinetics and other physical variables such as composition and specific surface area for a family of apatite and enamel samples. Several foreign agents (F, Sr, EHDP, EDTA, Mg) will also be studied both as entities of interest in their own right and as probes into the quantitative behavior of the unified apatite model. Aside from providing insights into the spectrum of mechanisms with which foreign agents can interact with apatite, these studies will also serve as a prototype for methodologies to be used in studying other foreign agents with the unified apatite model. Studies both with and without foreign agents will include the establishment of the regimes in which either subsurface lesions, gross cavitation, or no appreciable mineral loss is observed. The combination of the foreign agent data and the unified model to lead to predictions of lesion morphology as a function of solution composition and apatite type will be invaluable to our understanding of the mechanisms of dental caries formation.